Although many of the traditional cryptographic techniques may be applicable to wireless communications, these techniques suffer from the problem that the legitimate parties rely on a computational difficulty of obtaining a key by an eavesdropper, as opposed to a mathematical impossibility. As computational power available for an eavesdropper increases, the effectiveness of such methods decreases. Additionally, such methods suffer from a problem that it is usually a simple matter to verify whether a particular guess is correct. Thus, it would be advantageous to construct a cryptographic technique that provides absolute secrecy, rather than one based on computational assumptions. Joint randomness not shared by others (JRNSO) is an example of a theoretical technology that provides absolute secrecy.
In JRNSO Alice and Bob are two wireless transmit receive units (WTRUs), which communicate with each other on a shared frequency. Due to channel reciprocity, channel measurements taken on reciprocal channels by each of the two WTRUs will be very similar if taken at approximately the same time.
If an attacker entity, Eve, is located more than half a wavelength away from either Alice or Bob, the channel measurements by Eve are almost certainly independent from the channel-specific measurements by Alice or Bob. JRNSO utilizes this independence to generate a shared random secret key; however, several challenges arise in implementing JRNSO.
In a proposed implementation of JRNSO, Alice and Bob estimate the channel impulse response (CIR) of the reciprocal wireless channel based on their received radio signals. The output of channel estimation is a CIR measurement, which is composed of highly correlated samples. The CIR measurements by Alice and Bob are then cross-correlated.
The raw CIR data obtained from the CIR data collection system may not be well synchronized, in addition one WTRU may collect more CIR measurements than the other, resulting in some CIR measurements that cannot be paired. Moreover, each collected CIR is composed of a plurality of samples, but not every sample contains useful information about the mutual wireless channel. Therefore it is desirable to provide a method and apparatus for synchronizing and post-processing raw CIR data.